DESCRIPTION: (Applicant's Abstract) The overall purpose of this research proposal is to identify the molecular basis underlying the functions of the CB2 cannabinoid receptor. One of the major problems for cannabinoids as therapeutic agents is their severe psychoactive side-effect. The recent cloning of CB2, a subtype of cannabinoid receptors, brought us new hope for a better medical use of cannabinoids. CB2 is distributed primarily in the peripheral tissues, whereas CB1 I distributed primary in the central nervous system. CB2 has only 44 percent amino acid identity with CB1. Recently several CB2-selective cannabinoid ligands have been discovered; the signal transduction pathway for CB2 is being identified; and the pharmacological properties of CB2 in a rat mast cell line, RBL-2H3 cells, have been shown to be different from those of the cloned human CB2. The hypotheses of this proposal include: 1. The ligand binding and signal transduction characteristics of CB2 are determined by its unique structural features. 2. The differences between RBL-2H3 cell cannabinoid receptors and human CB2 may be explained by either the structural differences between rat and human CB2, or the novel receptor subtypes that may exist in RBL-2H3 cells. The following specific aims will attempt to test these hypotheses: Specific Aim 1: To determine the amino acids of CB2 that are important for ligand binding. Specific Aim 2: To determine the amino acids of CB2 that are important for receptor activation. Specific Aim 3: To characterize cannabinoid receptor subtypes in a rat mast cell line (RBL-2H3). A combination of molecular cloning, mutagenesis, heterologous expression, and pharmacological assays will be utilized to test the hypotheses of this proposal. Molecular modeling studies will be performed collaboratively. These studies should help us to understand in more molecular detail the ligand binding and activation of cannabinoid receptor subtypes, particularly about CB2, which is a very important receptor for the immune-modulatory effects of marijuana and cannabinoids. Ultimately, this may facilitate the development of novel cannabinoid mimetics with improved therapeutic properties and minimized psychoactive side effects.